#358 Add future interface methods, remove exception throwing

- Create Utils class for a common implementation of md5/sha1
- Create "foolproof" way of getting the MessageDigest for md5 etc. (MessageDigestAlgorithm enum)
- Create description annotations to annotate algorithms with usage recommendation and salt type

src/main/java/fr/xephi/authme/security/MessageDigestAlgorithm.java

@@ -0,0 +1,30 @@
+package fr.xephi.authme.security;
+
+import java.security.MessageDigest;
+
+/**
+ * The Java-supported names to get a {@link MessageDigest} instance with.
+ *
+ * @see <a href="http://docs.oracle.com/javase/1.5.0/docs/guide/security/CryptoSpec.html#AppA">
+ *      Crypto Spec Appendix A: Standard Names</a>
+ */
+public enum MessageDigestAlgorithm {
+
+    MD5("MD5"),
+
+    SHA1("SHA-1"),
+
+    SHA256("SHA-256"),
+
+    SHA512("SHA-512");
+
+    private final String key;
+
+    MessageDigestAlgorithm(String key) {
+        this.key = key;
+    }
+
+    public String getKey() {
+        return key;
+    }
+}